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It's another world . . . but is it our 10th planet ?
By Louise Milligan and agencies
15mar04

SCIENTISTS have found a new world orbiting the solar system – more than 3 billion kilometres further away from the Sun than Pluto and 40 years away from Earth in a space shuttle.

NASA is expected to announce today the discovery of the space object, which some experts believe could be a new planet.

It is provisionally known as Sedna, after the Inuit goddess of the sea.

The discovery of Sedna – 10 billion kilometres from Earth – is a testament to the new generation of high-powered telescopes.

Measurements suggest Sedna's diameter is almost 2000km – the biggest find in the solar system since Pluto was discovered 74 years ago. It is believed to be made of ice and rock, and is slightly smaller than Pluto.

The find will reignite the debate over what constitutes a planet. Some scientists claim even Pluto is too small to count as one.

According to astronomer Michael Brown of the California Institute of Technology, who discovered Sedna, there could be many other new worlds orbiting the Sun and waiting to be discovered.

"Sedna is very big, and much further out than previous discoveries," he said. "I'm pretty sure there are other large bodies up there too."

But physicist and cosmologist Paul Davies, of Sydney's Macquarie University, said it was folly to describe Sedna as a planet. "It's fun, it's exciting, but let's keep it in proportion," Professor Davies said yesterday.

He said scientists had known for "a decade or so the solar system does not come to an abrupt halt" and there were a number of "planetessimals" or little planets, like Sedna.